1. Field of the Invention
The present invention relates to a process for preparing an aromatic polyhydric alcohol, and, in particular to a process for preparing an aromatic polyhydric alcohol by the catalytic hydrocracking of an aromatic polycarboxylic acid ester.
Aromatic polyhydric alcohols are useful as plasticizers, solvents for paint and varnishes, and raw materials for the production of pharmaceuticals and agricultural chemicals. In addition, they are useful as raw materials for manufacturing high molecular weight substances, i.e., polymeric substances, such as fibers, synthetic resins, and the like, and in particular, for manufacturing high molecular weight substances with high heat resistance.
2. Description of the Prior Art
The manufacture of alcohols by the catalytic hydrocracking of the corresponding carboxylic acid ester is commonly known. For example, in "Organic Reaction", Vol. VIII, pages 1-27, John Wiley & Sons, New York (1954), the reaction conditions for the production of alcohols and yields obtainable thereby when using Adkins-type catalyst containing Cu-Cr oxides as the main components are summarized by H. Adkins. However, the catalytic hydrocracking using an Adkins-type catalyst under high temperature and high pressure was originally developed for the purpose of producing aliphatic alcohols from corresponding aliphatic carboxylic acid esters. When this process is used without modification for catalytic hydrocracking of aromatic carboxylic acid ester, significant amounts of aromatic alcohols are excessively reduced to produce aromatic hydrocarbons.
British Patent No. 1,254,927 discloses a process intended to suppress such side reactions by using copper oxide containing one or more of the oxides or carbonates, or both, of metals selected from the group consisting of magnesium, calcium, strontium, and barium as the catalyst. Also, Japanese Patent Publication No. Sho 47(1972)-35419 discloses an aromatic alcohol production process of liquid phase hydrogenation in the presence of a mixed catalyst of copper and (1) strontium, or (2) zinc and chromium, or (3) nickel and magnesium. Further, Japanese Patent Publication No. Sho 49(1974)-31435 discloses a process for preparing an aromatic alcohol by catalytic hydrocracking of corresponding aromatic carboxylic acid ester by using a catalyst comprising copper oxide containing alumina, magnesia, and chromium oxide, or, a catalyst comprising copper oxide containing magnesia, chromium oxide, and iron oxide.
Although these catalysts mentioned above have been proposed for the process for catalytic hydrocracking of aromatic polycarboxylic acid ester, because the conversion rate of the aromatic polycarboxylic acid esters is low and the yield of the aromatic polyhydric alcohols is low, too, development of an improved process is desired.
Specifically, the conversion rate of esters in the British Patent No. 1,254,927 is about 50 to 80% and selectivity to alcohol is 40 to 70%, so that the yield of polyhydric alcohols obtained by this process is at best 60%. Also, in Japanese Patent Publication No. Sho 47(1972)-35419, the selectivity is slightly improved, but the conversion rate is 40% or less. The catalyst used in Japanese Patent Publication No. Sho 49(1974)-31435 has a high selectivity of about 80% or greater but the conversion rate is 70% or less.
Thus, processes heretofore proposed can only provide a low conversion rate of aromatic polycarboxylic acid esters. The yield of aromatic polyhydric alcohols obtained by these processes has been unsatisfactory, too. These drawbacks further necessitate several process steps for separation and purification of aromatic polyhydric alcohols from the reaction products.